1. Field of the Invention
Embodiments of the present invention generally relate to fire-fighting and more particularly to a foam for fighting fires in confined areas.
2. Description of the Related Art
Fires in confined areas can be extremely difficult to contain much less to extinguish due to a number of factors, for example, heat buildup, the availability of fuel, and the presence of toxic gases. These factors make delivery of fire suppressant material difficult. Hot combustion gases are confined and can be prone to explosion and can provide additional fuel to the fire. In addition, the combustion gases normally contain toxic levels of carbon monoxide gas, methane gas, and other toxic substances.
Examples of confined areas susceptible to fires are storage tanks, underground mines, and landfills. In coal mine fires, the abundance of fuel in a confined, poorly accessible area practically guarantees that the fire will burn for extremely long periods of time with resultant loss of production and great property loss. Many coal mines must be abandoned in the event of a fire because of the great difficulty in extinguishing the fire. For example, the Jonesville coal mine fire started more than 30 years ago and is still burning. The town of Centrala, Pa. has been abandoned because seeping of noxious gases to the surface from a coal mine fire that began in 1961. The residents of the City of Youngstown have seen their property values drop to near zero due to the Percy mine fire in Fayette County, Pa. that has been burning for more than 30 years and they are concerned that they will lose their homes.
Fighting a fire in a mine in general comprises the steps of (i) creating a seal between the portion of the confined area involved in the fire and the uninvolved portion of the confined area; and (ii) introducing a fire suppressant or allowing the fire to burn itself out while maintaining the involved area sealed. Typically, the atmosphere of the involved area is drawn out after it has been sealed. In many cases, however, removing the atmosphere from the involved area is not possible or practical. In addition, the involved area is often flooded with water to attempt to extinguish the fire and generally reduce the temperature at the involved area.
Permanent and temporary seals or brattices are well known and have been long used in the mining field for sealing portions of a passage or shaft in a mine. Brattices of varying designs are used to for ventilation control and for emergencies, such as in the event of a fire. The brattice is fire proof and provides a suitable opening to permit the distribution of fire suppressant to the area involved in the fire. A discussion of several different brattice designs is found in the '294 patent.
In mine fires where the involved area is sealed, it is preferred that the atmosphere in the sealed area is drawn out so as to reduce as much as possible the oxygen in the sealed area to limit or slow the progress of the fire. This may followed by an attempt to flood the area with water. In the fires at Centralia, Percy, and Jonesville mines, described above, these procedures alone did not work with the resultant loss to the community and to the mine operators.
Water is not the most effective fire suppressant or extinguishing material for use in most confined area fires, particularly in fighting coal mine fires. In many cases the water does not reach the fire because of dips and fissures in the mine shaft that in effect pool, retain, or otherwise divert the water and prevent it from reaching the fire. In addition, the contact time of water that does reach the fire is short and the water evaporates and does not thoroughly penetrate and/or wet the fuel supporting the fire.
Conventional foam has been applied in attempting to extinguish coal mine fires. This foam is expanded with air that, of course, contains a substantial concentration of oxygen thus adding a highly combustible substance to the fire that becomes available to support combustion as the foam breaks down.
Other techniques include injecting carbon dioxide and/or nitrogen. Nitrogen can be used either in gaseous form or by being mixed with a surfactant and water to produce high expansion foam. The foam is used to suppress the fire as well as forming a barrier to direct gas flows around the mine. However, since the densities of nitrogen and carbon dioxide are substantially the same or greater than that of air, the injected gas/foam will not affect fires burning in the roofs of caverns unless the entire involved area is flooded with the gas or foam. Such an operation requires heavy equipment and a substantial amount of time. In one instance, a jet engine was used to suppress such a fire by injecting an entire mine with carbon dioxide.
Although not prone to the extremely long burning periods encountered in coal mine fires, other fire locations such as underground fuel storage tanks, above ground chemical storage tanks and the like present similar problems. It is difficult to apply fire suppressant material to the fire because of the danger to the firefighters from explosion, heat buildup and toxic gases.
Therefore, there exists a need in the art for an improved fire suppressant for fighting fires in confined areas.